Because the horizontal output circuits of a television receiver contain very high voltages and currents when in operation, it is difficult to analyze such circuits when using the methods and instruments heretofore known in the prior art. The older television receivers allowed a service technician to reduce the voltages and currents in the horizontal output circuits by lowering the applied AC power voltage with the aid of a variable AC power source. However, many present day television receivers incorporate Switch Mode power supplies which strive to maintain a constant level of internal voltage irrespective of changes in the input AC voltage level. Also, contemporary televisions receivers include a Safety Shutdown circuit which deenergizes the television receiver when the level of voltage applied to the picture tube could cause hazardous levels of radiation from the picture tube. These two developments in television receiver design have made it virtually impossible to troubleshoot the horizontal output circuits using conventional techniques without endangering the service technician and the components of the television receiver.
The horizontal output stage of a television receiver is the main current load on the B+ power supply and is responsible for developing the high voltage for the cathode ray picture tube. Problems in the horizontal output stage or in the flyback transformer secondary circuits typically increase the current demand from the B+ power supply and/or alter the timing of the horizontal output stage. Since the horizontal output stage operates at voltage levels as high as 1500 volts and current levels as high as 1.5 amps, extreme care must be used during any circuit analysis being made while these very high normal voltage and current levels exist.
Since it is important to test the horizontal output circuits of present day television receivers, it would be desirable to provide an instrument and method for safely testing these circuits.